1. Field of the Invention
The present invention relates to a phosphor composition used for a fluorescent lamp and a fluorescent lamp using the same.
2. Description of the Related Art
Conventionally, an antimony-/manganese-coactivated calcium halophosphate phosphor is most widely used for a general illumination fluorescent lamp. Although a lamp using such a phosphor has a high luminous efficiency, its color rendering properties are low, e.g., a mean color rendering index Ra=65 at a color temperature of 4,300 K of the luminescence spectrum of the phosphor and a mean color rendering index Ra=74 at a color temperature of 6,500 K. Therefore, a lamp using such a phosphor is not suitable when high color rendering properties are required.
Japanese Patent Publication No. 58-21672 discloses a three component type fluorescent lamp as a fluorescent lamp having relatively high color rendering properties. A combination of three narrow-band phosphors respectively having luminescence peaks near 450 nm, 545 nm, and 610 nm is used as a phosphor of this fluorescent lamp.
One of the three phosphors is a blue luminescence phosphor including, e.g., a divalent europium-activated alkaline earth metal aluminate phosphor and a divalent europium-activated alkaline earth metal chloroapatite phosphor. Another phosphor is a green luminescence phosphor including, e.g., a cerium-/terbium-coactivated lanthanum phosphate phosphor and a cerium-/terbium-coactivated magnesium aluminate phosphor. The remaining phosphor is a red luminescence phosphor including, e.g., a trivalent europium-activated yttrium oxide phosphor. A fluorescent lamp using a combination of these three phosphors has a mean color rendering index Ra=82 and a high luminous efficiency.
Although the luminous flux of such a three component type fluorescent lamp is considerably improved compared with a lamp using the antimony-/manganese-coactivated calcium halophosphate phosphor, its color rendering properties are not satisfactorily high. In addition, since rare earth elements are mainly used as materials for the phosphors of the three component type fluorescent lamp, the phosphors are several tens times expensive than the antimony-/manganese-coactivated calcium halophosphate phosphor.
Generally, a fluorescent lamp using a combination of various phosphors is known as a high-color-rendering lamp. For example, Japanese Patent Disclosure (Kokai) No. 54-102073 discloses a fluorescent lamp using a combination of four types of phosphors, e.g., divalent europium-activated strontium borophosphate (a blue luminescence phosphor), tin-activated strontium magnesium orthophosphate (an orange luminescence phosphor), manganese-activated zinc silicate (green/blue luminescence phosphor), and antimony-/manganese-coactivated calcium halophosphate (daylight-color luminescence phosphor). In addition, a lamp having Ra&gt;95 has been developed by using a combination of five or six types of phosphors. However, these high-color-rendering lamps have low luminous fluxes of 1,180 to 2,300 Lm compared with a fluorescent lamp using the antimony-/manganese-coactivated calcium halophosphate phosphor. For example, a T-10.40-W lamp using the antimony-/manganese-coactivated calcium halophosphate phosphor has a luminous flux of 2,500 to 3,200 Lm. Thus, the luminous efficiencies of these high-color rendering fluorescent lamps are very low.